"And you have to ask yourself why Mr Turnbull is less willing to act than Mr Abbott was. The only possible conclusion is that the PM, Mr Turnbull, needs to protect his numbers man in the face of a resurgent right wing of the Liberal Party."

Plibersek said there were many issues that Sinodinos needed to address about his time at the senior Liberal post.

"I think there's certainly questions around the individual role that Senator Sinodinos has played as the treasurer and finance director of the NSW branch of the Liberal Party while illegal donations were being channelled through the Free Enterprise Foundation," she said.

"There are questions around Senator Sinodinos' individual behaviour, there are certainly questions about the NSW branch of the Liberal Party."

Wow. Senator Arthur Sinodinos has released a seven page letter through his lawyers on Good Friday at 10pm... pic.twitter.com/f9aQYtmAYi